My guess its simply something as silly as the on/off button, or wiring. Try removing the MB connector for the PSU on/ff switch, and just short the appropriate pins with a screwdriver. If that doesn't work, then your MB is most likely toast, as it does not give a "PWR OK" signal back to the PSU. There is no other reason I can think off that would keep at least the PSU from activating.. unless.. are you sure you are having power on the wall socket ?
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